Tubular, electrical, heating element with bulkhead fitting



Nov. 21, 1967 L. T. KOLLAR ET AL I 3,354,294

TUBULAR, ELECTRICAL, HEATING ELEMENT WITH BULKHEAD FITTING Filed Sept. 7, 1965 INVENTORS. Ly/e T 0//0/ gay/77000 5. \Sfufsman Maw ATTORNEY United States Patent 3,354,294 TUBULAR, ELECTRICAL, HEATING ELEMENT WITH BULKHEAD FITTING Lyle T. Kollar and Raymond S. Stutsman, Allegan, Mich.,

assignors to Tru Heat Corporation, Allegan, Mich.

Filed Sept. 7, 1965, Ser. No. 485,299 Claims. (Cl. 219-536) ABSTRACT OF THE DISCLDSURE An electrical heating element of the type having a resistance wire enclosed in a tubular metal sheath, with a low resistance connector wire connected to the resistance wire within the sheath and extending out of the end of the sheath; a fitting for connecting the end of the heating element in supported and sealed relation through a wall of a tank consisting of a tubular element sleeved in close fitting relation over the end of the sheath with the sheath terminating within the fitting and the connector wire projecting from the outer end of the fitting, a radially projecting flange on the inner end of the fitting with the inner end of the fitting adjacent to the sheath upset axially outwardly and radially inwardly into annular and slightly deforming sealing contact with the surface of the sheath, and a mass of electrically insulating sealing resin filling the outer end of the fitting around the connector pin and entering into the end of the sheath and the narrow clearance between the inside of the fitting and the outside of the sheath; the fitting being externally threaded on its outer end.

A modification has an interior annular groove in the fitting with a flexible O-ring seal in the groove engaged with the surface of the sheath.

A method of forming the annular upset in the fitting by backing the fitting with an annular abutment against the outer side of the flange and pressing an arcuate upsetting die with a wedge shaped cross section against the inner side of the flange and around the sheath is disclosed.

This invention resides in the electrical arts. It relates to tubular, electrical heating elements.

A tubular, electrical heating element is a structure for generating heat, which comprises a length of electrical resistance wire covered by thermally conductive, electrically nonconductive material and a thermally conductive, usually metallic, sheath. Tubular, electrical heating elements are commonly employed in water tanks, moisture containing compartments and the like. Consequently, tubular type electrical heating elements are frequently provided with one or two bulkhead fittings which enable such elements to be mounted on bulkheads and to pass from the moisture side of the bulkhead through the bulkhead to exterior electrical connections. In most cases it is necessary that the tubular, electrical heating element and each bulkhead fitting employed therewith be connected together and that the connection be mechanically strong and form a water tight seal. Heretofore, such a connection has been obtained by brazing the bulkhead fitting to the sheath of the heating element. A common solder employed for this purpose is silver solder. While this type of construction has been satisfactory, it has a cost disadvantage because of the soldering material and because of the brazing step.

An object of this invention is to provide a tubular, electrical heating element and bulkhead fitting structure which avoids this disadvantage.

This object and such other objects as may appear hereinafter are achieved by this invention which, in summary, comprises a tubular, electrical heating element with at least one bulkhead fitting connected thereto, said fitting 3,354,294 Patented Nov. 21, 1967 2 being anchored to said heating element by a portion of the wall of the fitting surrounding the sheath of said heating element, which portion is inwardly deformed and upset or wedged against the exterior surface of said sheath and forms thereby a water tight seal and a mechanically strong joint.

This invention is further described relating to the figures in the drawing, which comprise a material part of the disclosures herein. In the drawing:

FIG. 1 is a plan view of a specific embodiment of a preferred, tubular, electrical heating element and bulkhead fitting structure of this invention mounted on, and extending through, a bulkhead shown in cross section;

FIG. 2 is a longitudinal, sectioned view of a portion of the heating element and fitting structure of FIG. 1, which view has been taken as indicated by the sectioning line 2 2 of FIG. 1;

FIG. 3 is a longitudinal, sectioned view of part of another specific embodiment of a preferred, tubular, electrical heating element and bulkhead fitting structure of this invention, which view has been taken as though along the lines 2-2 of FIG. 1;

FIG. 4 illustrates one step in the assembly of the specific embodiment of the element and fitting structure of FIG. 2;

FIG. 5 illustrates another step in the assembly of the specific embodiment of the heating element and bulkhead fitting structure of FIG. 3, and

FIG. 6 is an enlarged view showing the deformed portion of the bulkhead fitting upset against the sheath of the heating element.

In greater detail, FIG. 1 illustrates a tubular, electrical heating element 10 of this invention. The heating element 10 has two ends. Anchored to the heating element at both ends are threaded bulkhead fittings 12. Each fitting 12 is disposed in a hole 14 through a bulkhead 16 and is secured to the bulkhead 16 by means of a gasket 18 and a lock nut 20 threadedly mounted on the threaded bulkhead fitting 12.

The tubular, electrical heating element 10 comprises an electrical resistance wire (not shown). In the region of each end of the heating element 10 the corresponding end of the wire is connected to a low resistance wire or conductor 22 referred to as a terminal pin, which extends outwardly from the end of the heating element 10. The resistance wire and part of each terminal pin 22 within the heating element 10 are covered by a normally thermally conductive, electrical insulation 24 encased in a metallic sheath 26. Preferred materials of construction for the sheath include copper, steel, stainless steel, nickel alloys such as Inconel, Incoloy, and the like. In cross section the heating element 10 is generally round. However, under the concepts of this invention the cross sectional shape of the heating element can be Whatever is desired. Each end of the metallic sheath 26 is within a corresponding bulkhead fitting 12. The underlying, thermally conductive, electrical insulation 24 likewise terminates at each end of the heating element 10 within the corresponding bulkhead fitting 12.

As shown in FIG. 2, each bulkhead fitting 12 comprises a cylindrical body 28 having at one end thereof an outwardly extending flange portion 30. The exterior of the cylindrical body 28 is threaded for receiving in threaded engagement a lock nut 20.

The longitudinal length of the cylindrical body 28 from the flange portion 30 to the unflanged end thereof should be at least equal to the thickness of thebulkhead 16 plus the thickness of the gasket 18 plus that dimension which will accommodate at least part of the lock nut 20. Preferred materials of construction for the fitting 12 include copper, brass, steel, stainless steel, and the like. Longitu- 3 dinally the bulkhead fitting 12 defines as shown in FIG. 4 a longitudinal passageway 32 extending from one end of the fitting to the other end. The cross sectional profile or shape of the longitudinal passageway 32, prior to anchoring the fitting 12 to the heating element is substantially the same as the exterior shape or cross sectional profile oft-he heating element 16, and the terminal end portion of the heating element 10 before anchoring the fitting 12 to the heating element 10 is in sliding fit with'the longitudinal passageway 32 through the fitting 12. The sheath 26 of the heating element 10 terminates within the longitudinal passageway 32 of the fitting 12 approximately midway between the ends of the longitudinal passageway 32. Preferably, the thermally conductive, electrical insulation 24 terminates within the longitudinal passageway 32 defined by the fitting 12, but short of the corresponding end of the sheath 26. The terminal pin 22'extends coaxially through, and outwardly from, the longitudinal passageway 3 2. The fitting 12 is mechanically connected to the sheath 26 of the heating element 10 by an inwardly deformed or crimped inner peripheral wedge portion 34 of the wall of the fitting 12, which wall defines the longitudinal passageway 32. As best shown in FIG. 6, the wedge portion 34 is upset into the residual space between the sheath 26 and the wall of the longitudinal passageway'and provides thereby a water tight seal and a strong, mechanical connection. Preferably, the wedge portion 34 is in the flange portion 30 of the fitting 12. Preferably the space from the ends of the normally thermally conductive, electrical insulation 24 and the sheath 26 to the open end of the fitting 12 and about the terminal pin 22 is filled with a normally electrically nonconductive sealant material 36 which bonds to the inner peripheral wall defining the longitudinal passageway 32 through the fitting 12, to the terminal 22, the sheath 26 and the normally thermally conductive, electrical insulation 24, whereby the sealant material 36 functions as a water tight sealand as an auxiliary fastener of the fitting 12 to the electrical heating element 10. Preferred examples of 'a suitable, sealant material 36 include such materials as epoxy resins, silicone sealants and the like.

The bulkhead fitting and heating element assembly shown in FIG. 2 is normally satisfactory for use under moderate conditions. However, for extreme conditions including substantial water pressures, the heating element and bulkhead fitting assembly of FIG. 3 is preferred. The basic structure of this assembly is substantially the same as the basic structure in the assembly of FIG. 2. However, this assembly comprises a bulkhead fitting 37 which in the flange portion 30 between the wedge part 34 and the terminal pin end of the fitting 12, comprises a continuous groove 38 in the wall defining the longitudinal passageway 32. Seated in the continuous groove 38 and extending inwardly towards the longitudinal axis of the passageway 32 so as to press against the sheath 26 is a strip 40 of resilient material such as, for example, silicone, rubber, polytetrafluoroethylene resin material, polydifiuorodichloroethylene resin material or the like. In specific embodiments of the fitting element assembly of FIG. 3, wherein the longitudinal passageway 32 and the sheath 26 are circular in cross section, the continuous groove 38 is an annular groove and the continuous strip 40 of resilient material is an O-ring.

The heating element and bulkhead fitting assembly of this invention is put together as follows. As indicated in FIG. 4 one end of a heating element 10 with the terminal pin 22 extending outwardly therefrom and with an end segment of the thermally conductive, electrical insulation 24 removed from under the sheath 26 is inserted into the longitudinal passageway 32 at the flanged end of the bulkhead fitting 12. The end of the sheath 26 is positioned about midway between the flanged end of the bulkhead fitting 12 and the opposite open end. Then, as indicated in FIG. 5, the fitting 12 is clamped as by clamp means 42 and a two part staking die 44 which, in position, closely surrounds the sheath 26 of. the hea g m l i 1.0 and has a substantially continuous, deforming portion or lip 4'6that is adjacent the sheath and faces the flanged end of the bulkhead fitting 12, is forced into the flanged end of the bulkhead fitting 12. The lip 46 of the staking die 44 displaces material from the wall about the passageway 32. This displaced material is forced into the longitudinal passageway 32 and is wedged or jammed against the heating element sheath 26, forming with the sheath 26 a mechanical, moisture tight seal. Thereafter, the sealant 36 is introduced into the space about the terminal pin 22 from the ends of the sheath 26 and thermally conductive, electrical insulation 24 to the open end of the longitudinal passageway 32. In preferred embodiments of this invention the sealant 36 is obtained in liquid form and is poured or injected into this spaceand permitted to solidify and harden, forming thereby a moisture tight seal at the end of the fitting 12. Either the two part staking die 44, or the opposed backing die 42 may be movable. Note that the backing die 42 closely surrounds the neck of the fitting and abuts against the flange portion 30 and the opposite end of the threaded portion 18. Note that the sealant extends to between the outer surface of the sheath and the opposed surface of the passageway, and that the surface of the sheath is deformed slightly as appears best in FIG. 6.

The heating element and bulkhead fitting assembly illustrated in FIG. 3 is made by the same procedure except that the continuous strip 40 of resilient material is inserted into the continuous groove 38 in the inner wall of the fitting 37 before the end of the heating element 10 is inserted into the longitudinal passageway 32.

Thus, this invention provides a tubular, electrical heating element with at least one bulkhead fitting connected thereto and forming therewith a mechanically strong, moisture tight seal. The seal is obtained without brazing and involves only a staking die and clamp means. Hence, the heating element and bulkhead fitting assembly of this invention has the advantage of reduced costs of materials and manufacturing. For example, the process of making the assembly eliminates the need for sand blasting the parts prior to brazing or soldering the connection, and the brazing or soldering materials. It also eliminates the cleaning step necessary after soldering or brazing to remove flux used in the soldering and brazing. It also provides a brighter, undiscolored appearance of the bulkhead fitting, which becomes important when the fitting is exposed as in the bottom of an open tank such as a dishwasher.

Other features, advantages and specific embodiments of this invention will be readily apparent to those in the exercise of ordinary skill in the art after reading the foregoing disclosures. In this regard, while specific embodiments of this invention have been described in considerable detail, variations and modifications of these embodiments can be eifected without departing from the spirit and scope of invention as disclosed and claimed.

We claim:

1. A tubular, electrical heating element and bulkhead fitting assembly comprising a tubular, electrical heating element and a bulkhead fitting anchored thereto, said heating element comprising a sheath and said bulkhead fitting comprising a generally cylindrical body having a longitudinally disposed passageway therethrough with the cross sectional profile of said passageway conforming substantially to the cross sectional profile of said sheath, said sheath prior to the anchoring of said fitting thereto being disposed substantial-1y in sliding fit in said passageway, said fitting being anchored to said sheath by an inwardly extending, peripheral wedge portion of the body wall defining said longitudinal passageway at one end. thereof, said wedge portion being upset into the space between the exterior surface of said sheath and said body wall defining said longitudinal passageway, said fitting having a radially inwardly opening annular groove formed therein and located in said passageway axially outwardly from said wedge portion, and an annular ring of resilient material located in said groove and bearing in sealing engagement around the exterior of said sheath.

2. A tubular, electrical heating element and bulkhead fitting assembly comprising a tubular, electrical heating element with a bulkhead fitting anchored thereto, said heating element comprising a resistance wire connected at one end to a terminal pin, normally thermally conductive, electrical insulation covering said resistance wire and the resistance wire connecting end portion of said terminal pin, and a sheath covering said insulation, said terminal pin extending coaxially through and outwardly from one end of said sheath with said insulation terminating within the region of said end of said sheath, said bulkhead fitting comprising a generally cylindrical body having a flanged end portion, the exterior of said body being threaded from the other end of said body substantially to said flanged end portion for receiving in threaded engagement a threaded lock nut, said body defining a longitudinal passageway from the flanged end to the other end of said body, the cross sectional profile of said passageway conforming substantially to the cross sectional profile of said sheath with said sheath prior to the anchoring of said fitting thereto beng disposed substantially in sliding fit in said passageway and ending in said passageway between the ends thereof with said terminal pin extending outwardly coaxially through and from said other end of said body, said fitting being anchored to said sheath by an inwardly extending, peripheral wedge portion of the flanged end portion of the body wall defining said passageway, said wedge portion being upset into the space between the exterior surface of said sheath and the interior surface of said body wall defining said passageway, and a normally electrically nonconductive sealant occupying the space between said terminal pin and said body wall defining said passageway from said other end of said body to said sheath and said insulation, and adhering to said body wall, terminal pin, sheath and insulation.

3. A tubular, electrical heating element and bulkhead fitting assembly according to claim 2, which comprises a continuous strip of resilient material bearing in sealing relationship against the exterior surface of said sheath and seated in a continuous groove in the body wall defining said passageway, said groove being adjacent said wedge portion on the side thereof towards said other end of said body.

4. A tubular, electrical heating element and bulkhead fitting assembly comprising a tubular, electrical heating element and a pair of bulkhead fittings anchored thereto, one at one end of said element, the other at the other end of said element, said heating element comprising a resistance wire with one end connected to a terminal pin and the other end connected to another terminal pin, normally thermally conductive, electrical insulation covering said resistance wire and the resistance wire connecting end portion of each of said terminal pins, and a sheath covering said insulation, said sheath having a substantially round periphery in cross section, one of said terminal pins extending coaxially through and outwardly from one end of said sheath with said insulation terminating within the region of said end of said sheath, the other of said terminal pins extending coaxially through and outwardly from the other end of said sheath with said insulation terminating within the region of said other end of said sheath, each of said bulkhead fittings comprising a generally cylindrical body having a flanged end portion, the exterior of said body being threaded from the other end of said body substantially to said flanged end portion for receiving in threaded engagement a threaded lock nut, said body defining a longitudinal passageway from the flanged end to the other end of said body, said passageway being round in cross section, with said sheath in each case being disposed substantially in sliding fit in said passageway and ending in said passageway between the ends thereof with said terminal pin in each case extending coaxially through and outwardly from said other end of said body, said fitting in each case being anchored to said sheath by an inwardly extending, circumferential wedge portion of the flanged end portion of the body wall defining said passageway, said Wedge portion being jammed into the annular space between the exterior surface of said sheath and the interior surface of said body wall defining said passageway, and in each case normally electrically nonconductive sealant occupying the space between said terminal pin and said body wall defining said passageway from said other end of said body to said sheath and said insulation, and adhering to said body wall, terminal pin, sheath and insulation.

5. A tubular, electrical heating element and bulkhead fitting assembly according to claim 4, which comprises an O-ring of resilient material bearing in sealing relationship against the exterior surface of said sheath and seated in an annular groove in the body wall defining said passageway, said groove being adjacent said wedge portion on the side thereof towards said other end of said body.

References Cited UNITED STATES PATENTS 2,785,270 3/1957 Burger 174-152 2,810,815 10/1957 Dicome 219-336 3,116,401 12/1963 Drugmand 219-542 3,134,889 5/1964 Drugmand 219526 3,209,123 9/1965 Windsor 219--208 3,210,526 10/1965 Burger 2193 18 3,217,138 11/1965 Drugmand 219-336 RICHARD M. WOOD, Primary Examiner. ANTHONY BARTIS, Examiner. VQLODYMYR Y, MAYEWSKY, Assistant Examiner. 

1. A TUBULAR, ELECTRICAL HEATING MEANS AND BULKHEAD FITTING ASSEMBLY COMPRISING A TUBULAR, ELECTRICAL HEATING ELEMENT AND A BULKHEAD FITTING ANCHORED THERETO, SAID HEATING ELEMENT COMPRISING A SHEATH AND SAID BULKHEAD FITTING COMPRISING A GENERALLY CYLINDRICAL BODY HAVING A LONGITUDINALLY DISPOSED PASSAGEWAY THERETHROUGH WITH THE CROSS SECTIONAL PROFILE OF SAID PASSAGEWAY CONFORMING SUBSTANTIALLY TO THE CROSS SECTIONAL PROFILE OF SAID SHEATH, SAID SHEATH PRIOR TO THE ANCHORING OF SAID FITTING THERETO BEING DISPOSED SUBSTANTIALLY IN SLIDING FIT IN SAID PASSAGEWAY, SAID FITTING BEING ANCHORED TO SAID SHEATH BY AN INWARDLY EXTENDING, PERIPHERAL WEDGE PORTION OF THE BODY WALL DEFINING SAID LONGITUDINAL PASSAGEWAY AT ONE END THEREOF, SAID WEDGE PORTION BEING UPSET INTO THE SPACE BETWEEN THE EXTERIOR SURFACE OF SAID SHEATH AND SAID BODY WALL DEFINING SAID LONGITUDINAL PASSAGEWAY, SAID FITTING HAVING A RADIALLY INWARDLY OPENING ANNULAR GROOVE FORMED THEREIN AND LOCATED IN SAID PASSAGEWAY AXIALLY OUTWARDLY FROM SAID WEDGE PORTION, AND AN ANNULAR RING OF RESILIENT MATERIAL LOCATED IN SAID GROOVE AND BEARING IN SEALING ENGAGEMENT AROUND THE EXTERIOR OF SAID SHEATH. 